The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
One application of an industrial high-side switch is to drive a coil (or inductor) of an electromagnetic relay. During an “ON” phase, the high-side switch delivers current to the coil. The coil generates magnetic force to keep contacts of the electromagnetic relay closed. When the electromagnetic relay is opened, it is desirable to transition the coil current to zero as fast as possible in order to preserve the electromagnetic relay (referred to herein as “fast demagnetization”).
Fast demagnetization may be accomplished by making the switch behave as a high-voltage Zener diode, which clamps a voltage of the coil at about VZener=50V below VDD. For example with a power supply voltage VDD=30V, the inductance of the coil will see a reverse voltage of VDD−VZener=−20V, which will drive the inductance demagnetization.
During fast demagnetization, a discharge circuit generates thermal power (P=VZener*Iinductor) that can become very high when large relays are used (e.g. P=50 W). As a consequence, the IC will heat up quickly. Unfortunately, the coil current cannot be stopped while it is flowing. Therefore, the high-side switch needs to rely solely upon the power dissipation capability of the IC package to maintain the temperature of the IC until the coil is completely discharged. Above a certain energy level (depending on the size of the electromagnetic relay and on the initial current), the high-side switch eventually fails and is permanently damaged.